Partner of journalist who revealed NSA documents detained by British security

Journalist Glenn Greenwald, left, greets his partner David Miranda at Rio de Janeiro's International Airport on Monday.

The partner of Glenn Greenwald — the journalist who first revealed classified documents provided by ex-National Security Agency contractor Edward Snowden — was detained by British security officials and questioned for nearly nine hours at Heathrow Airport outside London Sunday.

Greenwald, who writes for the U.K.-based Guardian newspaper, told NBC News that he was called early Sunday morning by a British security official and informed that authorities had detained David Miranda, with whom he lives in Rio de Janeiro, Brazil, under a provision of a British anti-terrorism law that permits authorities to stop, search, question and detain individuals at airports, ports and border areas.

"They questioned (Miranda) about my journalism," Greenwald said.

According to Greenwald, they also asked Miranda for the password to his laptop computer, and what he knew about the documents that Snowden had provided to Greenwald and documentary filmmaker Laura Poitras.

Miranda was passing through London on his way back from Berlin, where he had been meeting with Poitras.

According to the Guardian, British authorities also confiscated Miranda's laptop, mobile phone, camera, memory sticks, DVDs and games consoles.

The Guardian's Glenn Greenwald has been reporting on Edward Snowden's revelations about the NSA's secret surveillance program. He joins Andrea Mitchell to talk about Snowden's new life in Russia.

"We were dismayed that the partner of a Guardian journalist who has been writing about the security services was detained for nearly nine hours while passing through Heathrow airport," the Guardian said in a statement provided to NBC News. "We are urgently seeking clarification from the British authorities."

Scotland Yard issued a brief statement about the detention of Miranda, a Brazilian national, saying he’d been held briefly under a provision of an anti-terrorism law.

"At 08:05 on Sunday 18 August 2013,” said the statement, "a 28-year-old man was detained at Heathrow Airport under Schedule 7 of the Terrorism Act 2000. He was not arrested. He was subsequently released at 17:00.”

Greenwald said the incident showed the U.S. government and its allies haven’t figured out exactly what Snowden took with him when he left Hawaii for Hong Kong in May.

"They definitely don’t know what Snowden took," he said.

The Brazilian government condemned Miranda’s detention and questioning in a statement published on the website of its foreign ministry.

"This measure is without justification since it involves an individual against whom there are no charges that can legitimate the use of that legislation," said the statement. "The Brazilian government expects that incidents such as the one that happened to the Brazilian citizen today do not repeat."